The invention relates to a belt driven fluid compressor and more particularly to a belt driven fluid compressor having a self-adjusting belt tensioning device that automatically maintains the required tension in the drive belt during compressor operation.
Rotary screw compressors traditionally include male and female rotors having interengaging, axially extending screw profiles. The rotors compress a fluid such as air, as the fluid is conveyed axially between the profiles during rotation of the rotors by a prime mover such as an electric motor. Typically, the male rotor includes an input element or shaft connected in motive force receiving relation with the output element or shaft of the prime mover by a drive belt tensioned with a predetermined required belt tension force.
Over time, the drive belt may stretch, or the distance between the output element and input element may change. Belt stretching and varying the distance between the input and output elements will cause the tension in the belt to deviate from the predetermined required tension. When the tension in the belt is not equal to the predetermined required tension value, the operation of the compressor is negatively affected. Therefore it is vital for efficient compressor operation that the predetermined required belt tension be maintained.
Helical springs have been included in prior art compressors to try to maintain the required drive belt tension. There are at least two shortcomings associated with using helical springs to maintain the required belt tension. First, by their design, the force exerted by any helical spring varies with its change in length. Therefore, the force exerted by each helical spring is dependent on its location relative to the belt. The helical springs are located in positions along the compressor that compress the springs the required amount to produce the total spring force necessary to achieve the required belt tension. However, as the belt stretches, and the springs decompress, the belt tensioning forces produced by the springs decrease resulting in a belt tension that is below the requisite tension force. When the drive belt is tensioned at less than the required tension force the belt is prone to slipping which reduces the efficiency of the compressor. Thus, during compressor operation the helical springs are not self-adjusting and do not continuously maintain the required belt tension in the drive belt.
A second shortcoming associated with the use of helical springs to maintain the required drive belt tension relates to the damping characteristics of helical springs. A helical spring has very little damping capacity and use of helical springs in fluid compressors can cause compressor components to oscillate or "bounce" under certain conditions, such as during compressor start up. Additionally, the helical springs do dissipate kinetic energy of the compressor components when a drive belt breaks.
Other known mechanisms for maintaining the required drive belt tension require periodic manual adjustment to maintain a constant belt tension over time. Such known systems frequently include an extendable and retractable member connected to a pulley, sprocket or other belt support member. When required, the length of the member is altered to move the belt support member and affect the belt tension. Such manually adjustable tension mechanisms are by their very nature not self-adjusting and do not automatically maintain the predetermined required belt tension.
Other known belt tensioning systems achieve the required belt tension through the use of complicated, expensive systems which frequently incorporate electronic controls to extend or retract hydraulic or pneumatic pistons to increase or decrease the belt tension to produce the desired tension in the drive belt.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.